In civil engineering terminology, a bridge is a structural unit or a series of structural units called spans which are designed primarily for the purpose of supporting moving loads in addition to the bridge's own weight. These structures are generally known to, provide means for foot, highway, rail or even horse traffic to pass from one location to another over water, ground depressions, railroad tracks and other obstacles which may impede traffic flow. The instant invention is utilized on non-movable spans. A non-movable span is a bridge which while moving, does not have the total span move such as a vertical lift bridge, a swing bridge which may rotate 90 degrees, or a bascule bridge which pivots about a horizontal access or rolls back on circular segments.
Bridges that are relatively long, and which cannot be made in a single span to stretch from one column or bent on one side of the obstacle, be it a river, a set of tracks, a road, etcetera to reach the other side of the obstacle, are constructed in a plurality of spans connected together these bridges are called multi-span structures. The type of material used for construction dictates the maximum length of a span between two bents. Because materials move by thermal expansion and contraction, joints must be incorporated into the design or the bridge will tear itself apart. The joints are in two main forms, over bent joint and a fully supported hinge.
One type of bridge construction is known as a box beam system, wherein a box beam will stretch from a first side of the span and from the second side of the span but the distance between is not covered by a single column, but rather by a junction of a plurality of columns. This type of bridge construction is known as hinge bridge construction and the hinge between the two portions is shaped like a pair of elements, one of which is shaped like a FIG. 7 the other of which is shaped like an L both of which rest against each other. This combined element is called the bridge hinge. This quadrilateral shaped element is known in the art as a Wichert truss.
A series of cables are used to hold the vertical and horizontal portions of the hinge together. In the case of earthquake, these cables will elongate and absorb the energy that may cause the bridge to fail. Prior to the Northridge, Calif. earthquake and for several years subsequent thereto, the cables from the hinge were replaced on a guesstimate basis as to whether or not they had in fact elongated due to the longitudinal stresses that may have been placed upon them. Once a cable has been stressed to cause it to elongate, the cable becomes strain hardened and is no longer usable for its intended purpose. It was found that there was indeed a need for a cable yield indicator to advise a bridge inspector when and as one or more of the cables of a hinge bridge had extended.
It is an object therefore of this invention to provide an indicator means that gives a positive indication as to when an earthquake restrainer cable of a hinge bridge has elongated.
It is another object of this invention to provide a positive means of detecting cable elongation due to earthquake forces.
It is yet another object to provide a low cost device that is light in weight and which will give a visual indication of the previous existence of a stressed condition in an earthquake restrainer cable.
It is a still further object to provide an easy to install device that will advise a bridge inspector that a restrainer cable has elongated due to earthquake forces.
It is an additional object to provide a device that provides a visual indication that a bridge's earthquake restrainer cable has elongated due to the stress suffered by the cable.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the device possessing the features properties and the relation of components which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the appended claims.
For a fuller understanding of the nature and objects of the invention reference should be made to the following detailed description, taken in conjunction with the accompanying drawings.